Ascorbic acid supplementation prevents hyperlipidemia and improves myocardial performance in streptozotocin-diabetic rats

The Changes in Endogenous Metabolites in Hyperlipidemic Rats Treated with Herbal Mixture Containing Lemon, Apple Cider, Garlic, Ginger, and Honey

An herbal mixture composed of lemon, apple cider, garlic, ginger and honey as a polyphenol-rich mixture (PRM) has been reported to contain hypolipidemic activity on human subjects and hyperlipidemic rats. However, the therapeutic effects of PRM on metabolites are not clearly understood. Therefore, this study aimed to provide new information on the causal impact of PRM on the endogenous metabolites, pathways and serum biochemistry. Serum samples of hyperlipidemic rats treated with PRM were subjected to biochemistry (lipid and liver profile) and hydroxymethylglutaryl-CoA enzyme reductase (HMG-CoA reductase) analyses. In contrast, the urine samples were subjected to urine metabolomics using 1H NMR. The serum biochemistry revealed that PRM at 500 mg/kg (PRM-H) managed to lower the total cholesterol level and low-density lipoprotein (LDL-C) (p < 0.05) and reduce the HMG-CoA reductase activity. The pathway analysis from urine metabolomics reveals that PRM-H altered 17 pathways, with the TCA cycle having the highest impact (0.26). Results also showed the relationship between the serum biochemistry of LDL-C and HMG-CoA reductase and urine metabolites (trimethylamine-N-oxide, dimethylglycine, allantoin and succinate). The study's findings demonstrated the potential of PRM at 500 mg/kg as an anti-hyperlipidemic by altering the TCA cycle, inhibiting HMG-CoA reductase and lowering the LDL-C in high cholesterol rats.

Combined effect of metformin with ascorbic acid versus acetyl salicylic acid on diabetes-related cardiovascular complication; a 12-month single blind multicenter randomized control trial

Background

We aimed to investigate the efficacy of ascorbic acid and acetylsalicylic acid among type II diabetes mellitus patients using metformin (only) for diabetes management therapy.

Method

A 12-month single blinded multicenter randomized control trial was designed to investigate the measured variables [Glycated Hemoglobin (HbA1c), Renal function, Albumin Creatinine Ratio (ACR) etc.]. The trial was randomized into 2 experimental parallel arms (ascorbic acid vs acetylsalicylic acid) were blinded with study supplements in combination with metformin and findings were compared to control arm with metformin alone and blinded with placebo. Withdrawal criteria was defined to maintain the equity and balance in the participants in the whole trial.

Finding

Patients with metformin and ascorbic acid (parallel arm I) was twice more likely to reduce HbA1c than metformin alone (control arm) in a year (OR 2.31 (95% CI 1.87–4.42) p < 0.001). Also Parallel arm I was ten times more likely to reduced risk factors contributing to long-term diabetes complications than participants of arm II in a year (OR 10.38 (95% CI 6.91–15.77) p < 0.001). In contrast, parallel arm II patients were seven times more effective to reduce the risk of expected CVD development in 10 years than arm I (OR 7.54 (95% CI 3.76–10.32) p < 0.001).

Conclusions

The trial concluded that ascorbic acid with metformin is more effective against reducing risks for diabetes related long-term complications (including ACR).

TRIAL details Registration No: NTR-6100, Registry Name: Netherlands Trial Registry, URL: http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=6100, Date of Registration: 20th October, 2016, Date of first Enrollment: 1 November, 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0584-9) contains supplementary material, which is available to authorized users.

Combined metoprolol and ascorbic acid treatment prevents intrinsic damage to the heart during diabetic cardiomyopathy

Metabolic disturbances and oxidative stress have been highlighted as potential causative factors for the development of diabetic cardiomyopathy. The β-blocker metoprolol is known to improve function in the diabetic rat heart and ameliorates the sequelae associated with oxidative stress, without lowering oxidative stress. The antioxidant ascorbic acid is known to improve function in the diabetic rat heart. We tested whether a combination of ascorbic acid and metoprolol treatment would improve function further than each drug individually. Control and streptozotocin-induced diabetic Wistar rats were treated with metoprolol (15 mg·(kg body mass)(-1)·day(-1), via an osmotic pump) and (or) ascorbic acid (1000 mg·(kg body mass)(-1)·day(-1), via their drinking water). To study the effect of treatment on the development of dysfunction, we examined time points before (5 weeks diabetic) and after (7 weeks diabetic) development of overt systolic dysfunction. Echocardiography and working-heart-perfusion were used to assess cardiac function. Blood and tissue samples were collected to assess the severity of disease and oxidative stress. While both drugs improved function, only ascorbic acid had effects on oxidative damage. Combination treatment had a more pronounced improvement in function. Our β-blocker + antioxidant treatment strategy focused on oxidative stress, not diabetes specifically; therefore, it may prove useful in other diseases where oxidative stress contributes to the pathology.

Mechanisms underlying the impaired contractility of diabetic cardiomyopathy

Cardiac dysfunction is a well-known consequence of diabetes, with sustained hyperglycaemia leading to the development of a cardiomyopathy that is independent of cardiovascular disease or hypertension. Animal models of diabetes are commonly used to study the pathophysiology of diabetic cardiomyopathy, with the hope that increased knowledge will lead ultimately to better therapeutic strategies being developed. At physiological temperature, left ventricular trabeculae isolated from the streptozotocin rat model of type 1 diabetes showed decreased stress and prolonged relaxation, but with no evidence that decreased contractility was a result of altered myocardial Ca²⁺ handling. Although sarcoplasmic reticulum (SR) Ca²⁺ reuptake appeared slower in diabetic trabeculae, it was offset by an increase in action-potential duration, thereby maintaining SR Ca²⁺ content and favouring increased contraction force. Frequency analysis of t-tubule distribution by confocal imaging of ventricular tissue labeled with wheat germ agglutinin or ryanodine receptor antibodies showed a reduced T-power for diabetic tissue, but the differences were minor in comparison to other models of heart failure. The contractile dysfunction appeared to be the result of disrupted F-actin in conjunction with the increased type I collagen, with decreased myofilament Ca²⁺ sensitivity contributing to the slowed relaxation.

Oral administration of vitamin C prevents alveolar bone resorption induced by high dietary cholesterol in rats

BACKGROUND

A high-cholesterol diet stimulates alveolar bone resorption, which may be induced via tissue oxidative damage. Vitamin C reduces tissue oxidative damage by neutralizing free radicals and scavenging hydroxyl radicals, and its antioxidant effect may offer the clinical benefit of preventing alveolar bone resorption in cases of hyperlipidemia. We examined whether vitamin C could suppress alveolar bone resorption in rats fed a high-cholesterol diet.

METHODS

In this 12-week study, rats were divided into four groups: a control group (fed a regular diet) and three experimental groups (fed a high-cholesterol diet supplemented with 0, 1, or 2 g/l vitamin C). Vitamin C was provided by adding it to the drinking water. The bone mineral density of the alveolar bone was analyzed by microcomputerized tomography. As an index of tissue oxidative damage, the 8-hydroxydeoxyguanosine level in the periodontal tissue was determined using a competitive enzyme-linked immunosorbent assay.

RESULTS

Hyperlipidemia, induced by a high-cholesterol diet, decreased rat alveolar bone density and increased the number of tartrate-resistant acid phosphatase-positive osteoclasts. The expression of 8-hydroxydeoxyguanosine was upregulated in the periodontal tissues. Intake of vitamin C reduced the effect of a high-cholesterol diet on alveolar bone density and osteoclast differentiation and decreased periodontal 8-hydroxydeoxyguanosine expression.

CONCLUSION

In the rat model, vitamin C suppressed alveolar bone resorption, induced by high dietary cholesterol, by decreasing the oxidative damage of periodontal tissue.

Upregulation of sodium-dependent vitamin C transporter 2 expression in adrenals increases norepinephrine production and aggravates hyperlipidemia in mice with streptozotocin-induced diabetes

The hyperglycemia and hyperoxidation that characterize diabetes lead to reduced vitamin C (L-ascorbic acid, AA) levels in diabetic humans and animals. We examined the possibility that diabetes-induced low plasma AA levels impair AA distribution to various tissues and that these changes are closely related to the development of diabetic complications. AA levels were markedly decreased in the plasma and increased in the adrenals of mice with streptozotocin (STZ)-induced diabetes. Consistently with these results, in [1-(14)C]AA accumulation assays, the efficiency of [1-(14)C]AA accumulation was significantly higher in the adrenals (which had the greatest ability to accumulate [1-(14)C]AA) of diabetic mice than in those of controls. Expression of sodium-dependent vitamin C transporter (SVCT)-2, a transporter of AA, was upregulated in diabetic adrenals. Furthermore, increased AA incorporation into the diabetic adrenals by SVCT-2 led to increased plasma norepinephrine, triglyceride and free fatty acid levels in mice with STZ-induced diabetes. Therefore, oversupplementation with AA could be deleterious in diabetic patients, because overexpression of adrenal SVCT-2 in diabetes could lead to excessive AA uptake, thus enhancing norepinephrine production and exacerbating some diabetic complications. Interestingly, however, treatment with AA dose-dependently abolished the increased expression of adrenal SVCT-2 and normalized the abovementioned plasma parameters in diabetic mice. These results suggest SVCT-2-mediated increases in AA uptake by the adrenals followed by excessive production of plasma norepinephrine may play a pivotal role in the development of diabetic complications.

N-acetylcysteine prevents nitrosative stress-associated depression of blood pressure and heart rate in streptozotocin diabetic rats

Previous studies have indicated that cardiovascular abnormalities such as depressed blood pressure and heart rate occur in streptozotocin (STZ) diabetic rats. Chronic diabetes, which is associated with increased expression of inducible nitric oxide synthase (iNOS) and oxidative stress, may produce peroxynitrite/nitrotyrosine and cause nitrosative stress. We hypothesized that nitrosative stress causes cardiovascular depression in STZ diabetic rats and therefore can be corrected by reducing its formation. Control and STZ diabetic rats were treated orally for 9 weeks with N-acetylcysteine (NAC), an antioxidant and inhibitor of iNOS. At termination, the mean arterial blood pressure (MABP) and heart rate (HR) were measured in conscious rats. Nitrotyrosine and endothelial nitric oxide synthase (eNOS) and iNOS expression were assessed in the heart and mesenteric arteries by immunohistochemistry and Western blot experiments. Untreated diabetic rats showed depressed MABP and HR that was prevented by treatment with NAC. In untreated diabetic rats, levels of 15-F(2t)-isoprostane, an indicator of lipid peroxidation increased, whereas plasma nitric oxide and antioxidant concentrations decreased. Furthermore, decreased eNOS and increased iNOS expression were associated with elevated nitrosative stress in blood vessel and heart tissue of untreated diabetic rats. N-acetylcysteine treatment of diabetic rats not only restored the antioxidant capacity but also reduced the expression of iNOS and nitrotyrosine and normalized the expression of eNOS to that of control rats in heart and superior mesenteric arteries. The results suggest that nitrosative stress depress MABP and HR following diabetes. Further studies are required to elucidate the mechanisms involved in nitrosative stress mediated depression of blood pressure and heart rate.

Effects of vitamin C on muscle glycogen and oxidative events in experimental diabetes

Streptozotocin (STZ) is an agent used in creating experimental diabetes. Varying findings have been reported about the striated muscle glycogen levels in diabetes. In this study, it was planned to observe interaction of vitamin C (AA), of which deficiency has been shown in diabetics, with soleus muscle glycogen levels and oxidative events on STZ-diabetic subjects.

MATERIAL AND METHOD

In the study, 38 male adult Wistar Albino rats with weights 200 +/- 20 g were used by separating them into four groups: Control, Vitamin C, Diabetes, Diabetes + Vitamin C. Body weights and fasting blood glucose were measured at the beginning and end of the experiment. AA, TBARS, GSH, NOx and glycogen levels of soleus muscles, and AA level of blood were measured. The results were compared using Anova variance and Mann-Whitney U tests. Results showed that AA levels in blood increased with vitamin C administration; AA, GSH and NOx levels in the muscle were low and MDA and glycogen levels were high in diabetics; and that vitamin C in the given dosage partially corrected these values. These results indicate that higher dosage than daily 20 mg/kg Vitamin C is required for being effective on metabolic and oxidizing events in diabetic rats.

Effect of a Novel Molybdenum Ascorbate Complex on Ex Vivo Myocardial Performance in Chemical??Diabetes Mellitus

BACKGROUND

The insulin-like action of metal complexes on target tissues, including the heart, has been reported in experimental diabetes mellitus. Since streptozotocin-induced diabetes is associated with insulin deficiency and left ventricular dysfunction, this study was designed to determine whether the novel metal complex molybdenum ascorbate [MoO(2)(aa)(2)] would improve cardiac function in this model of diabetes.

METHODS

Diabetes was induced in Sprague-Dawley rats (n = 6) following an intravenous injection of streptozotocin (60 mg/kg). After 8 weeks of diabetes, cardiac function was determined in isolated working hearts perfused with 11 mmol/L glucose, 1.2 mmol/L palmitate and 3% albumin. MoO(2)(aa)(2 )was added directly into the perfusate of working hearts at a concentration of 200 micromol/L for a period of 30 minutes. Age-matched control rats served as controls (n = 6).

RESULTS

Cardiac function, expressed as heart rate (HR) and aortic flow, was significantly decreased in diabetic hearts compared with control hearts. The diabetic state was associated with 23% and 60% reductions in HR and aortic flow, respectively. Short-term addition of MoO(2)(aa)(2) was beneficial and partially prevented the attenuation in diabetic rat heart function. MoO(2)(aa)(2 )increased HR by 15%, while aortic flow was increased by 85%. In control hearts, MoO(2)(aa)(2) had no effect on HR and increased aortic flow by 12%.

CONCLUSION

This study extends previous observations on the benefit of metal complexes in experimental diabetes. Our results indicate that short-term treatment with MoO(2)(aa)(2) partially reversed the left ventricular dysfunction associated with the streptozotocin model of diabetes.

A Newly Synthesised Molybdenum/Ascorbic Acid Complex Alleviates Some Effects of Cardiomyopathy in Streptozocin-Induced Diabetic Rats

BACKGROUND

Exogenous insulin does not prevent cardiac failure in patients with type 1 diabetes mellitus and a cardioprotective insulin mimic is greatly needed. Certain transition metals are known to act as insulin mimics and may be cardio- protective. In this study, the ability of a newly synthesised molybdenum/ascorbic acid complex to strengthen cardiac function was investigated.

METHODS AND DESIGN

Male CD rats were assigned to one of five groups: non-diabetic control, non-diabetic control treated with molybdenum/ascorbic acid complex, diabetic treated with sodium ascorbate, diabetic treated with molybdenum/ascorbic acid complex and untreated diabetics. Type 1 diabetes was induced by streptozocin injection. Once diabetes was confirmed, treatment was initiated by adding either the molybdenum/ascorbic acid complex or sodium ascorbate to the drinking water and continued for 6 weeks. Following the treatment period, the animals were terminated, and their hearts were excised and mounted in a working heart perfusion apparatus. Blood samples were taken for plasma glucose and plasma lipid level determination. Cardiac function was evaluated using 1 hour of low-flow ischaemic stress followed by 30 minutes of reperfusion.

RESULTS

Hearts from the animals treated with the molybdenum/ascorbic acid complex displayed the best aerobic performance of all the diabetic animals. Blood glucose levels and blood lipid levels were significantly lower in animals treated with the complex than in other diabetic animals. The group treated with the complex also had a lower drinking rate than the other diabetic groups. Furthermore, hearts from animals treated with the molybdenum/ascorbic acid complex showed a greater degree of recovery from low-flow ischaemia than any other group.

CONCLUSIONS

The molybdenum/ascorbic acid complex showed some significant insulin-mimic and cardioprotective effects. Further development of this complex could provide a drug useful for alleviating some of the cardiovascular problems associated with diabetes mellitus.

Short term effects of L-carnitine on serum lipids in STZ-induced diabetic rats

The aim of this study was to evaluate the effects of L-carnitine supplementation on serum triglyceride and total cholesterol levels in streptozotocin (STZ)-induced diabetic rats. Thirty-two male Wistar rats were divided into diabetic and diabetic-L-carnitine-supplemented groups. Diabetes was induced by injection of a single dose of streptozotocin (40 mg/kg, intraperitoneally) in citrate buffer. L-Carnitine was supplemented by IM injection of 100 mg/kg per day for 10 days. Serum glucose, triglyceride and total cholesterol levels were determined at days 0, 5 and 10. Rats receiving L-carnitine had lower triglyceride levels at both days 5 and 10 (P < 0.05). Total cholesterol levels in the carnitine-supplemented group were lower, but statistical significance was achieved only at day 10 (P < 0.05). These results suggest that L-carnitine exhibits hypotriglyceridemic and hypocholesterolemic effects in streptozotocin-induced diabetic rats. Clinical trials of L-carnitine supplementation on patients with diabetes induced hyperlipidemia must be further evaluated.

Pharmacological prevention of diabetic cataract

Cataract--opacification of the lens--is closely related to diabetes as one of its major late complications. This review deals with three molecular mechanisms that may be involved in the development of diabetic cataract: nonenzymatic glycation of eye lens proteins, oxidative stress, and activated polyol pathway in glucose disposition. Implications resulting from these mechanisms for possible pharmacological interventions to prevent diabetic cataract are discussed. The article reviews research on potential anticataract agents, including glycation inhibitors, antioxidants, and aldose reductase inhibitors. Information on possible benefits of putative anticataract agents comes from a variety of approaches, ranging from laboratory experiments, both in vitro and in vivo, to epidemiological studies in patients.

Exaggerated coronary reactivity to endothelin-1 in diabetes: reversal with bosentan

We previously demonstrated that chronic endothelin receptor blockade (with bosentan) improved functional cardiac performance in streptozotocin-diabetic rats, suggesting a novel role of endothelin-1 (ET-1) in modulating diabetic heart dysfunction. To gain insight into the mechanism(s) underlying this effect, we examined the coronary vascular responses to ET-1 in hearts from diabetic and control rats treated with or without bosentan. Rats were divided into control, control-treated, diabetic, and diabetic-treated groups. The control-treated and diabetic-treated groups received bosentan (100 mg x kg(-1) x d(-1)) for 8 weeks. Following treatment, hearts were isolated and perfused, and coronary reactivity to ET-1 was assessed by measuring the changes in coronary perfusion pressure in response to ET-1 (50 and 100 pM). Additionally, maximal coronary blood flow (assessed with 10(-5) M adenosine) was measured in isolated perfused hearts. The key observation is that coronary reactivity to ET-1 was significantly higher in the diabetic than the control rats. This effect was normalized in diabetic rats chronically receiving bosentan. Maximal coronary vasodilation did not differ between the four groups. In conclusion, the reactivity of ET-1 is altered in the isolated perfused coronary vascular bed from diabetic rats, and chronic ET receptor blockade restores this reactivity to control values. These observations provide a possible mechanism for the improvement in diabetic heart function observed after chronic bosentan treatment.

Therapeutic potential of anti-oxidants and diabetic retinopathy

Retinopathy, a severely disabling complication of diabetes mellitus, is today the leading cause of acquired blindness among young adults in developed countries. Good glycaemic control can attenuate the development of diabetic retinopathy but such metabolic control is often difficult to achieve and maintain and additional therapies need to be identified by which retinopathy can be prevented or arrested. Hyperglycaemia plays a critical role in the development and progression of retinopathy, but the mechanism by which hyperglycaemia results in the development of retinopathy is not clear. Oxidative stress is increased in the retina in diabetes. The possible sources of increased oxidative stress might include increased generation of free radicals or impaired anti-oxidant defence system. Dietary supplementation with anti-oxidants in animal models of diabetic retinopathy inhibits retinal metabolic abnormalities and retinal histopathology, suggesting that oxidative stress is associated with the development of retinopathy. The mechanism by which anti-oxidants inhibit retinopathy in diabetes warrants further investigation, but animal studies show that increasing the diversity of anti-oxidants provides significantly more protection than using any single anti-oxidant. Thus, supplementation with anti-oxidants represents an achievable adjunct therapy to help preserve vision in diabetic patients.

Diabetes-induced metabolic abnormalities in myocardium: effect of antioxidant therapy

Effects of hyperglycemia (both diabetes and experimental galactosemia) on cardiac metabolism have been determined. In addition, the effect of supplemental antioxidants on these hyperglycemia-induced abnormalities of cardiac metabolism has been investigated. Diabetes or experimental galactosemia of 2 months duration in rats significantly increased oxidative stress in myocardium, as demonstrated by elevation of thiobarbituric acid reactive substances (TBARS) and lipid fluorescent products in left ventricle. Activity of protein kinase C (PKC) was elevated in the myocardium, and the activities of (Na,K)-ATPase and calcium ATPases were subnormal. Administration of supplemental antioxidants containing a mixture of ascorbic acid, Trolox; alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium prevented both the diabetes-induced and galactosemia-induced elevation of oxidative stress and PKC activity, and inhibited the decreases of myocardial (Na,K)-ATPase and calcium ATPases. The results show that these metabolic abnormalities are not unique to diabetes per se, but are secondary to elevated blood hexose levels, and supplemental antioxidants inhibit these metabolic abnormalities. Our findings suggest that antioxidants inhibit abnormal metabolic processes that may contribute to the development of cardiac disease in diabetes, and offer a potential clinical means to inhibit cardiac abnormalities in diabetes.

Diabetes mellitus and cardiac function

Cardiovascular complications are the most common causes of morbidity and mortality in diabetic patients. Coronary atherosclerosis is enhanced in diabetics, whereas myocardial infarction represents 20% of deaths of diabetic subjects. Furthermore, re-infarction and heart failure are more common in the diabetics. Diabetic cardiomyopathy is characterized by an early diastolic dysfunction and a later systolic one, with intracellular retention of calcium and sodium and loss of potassium. In addition, diabetes mellitus accelerates the development of left ventricular hypertrophy in hypertensive patients and increases cardiovascular mortality and morbidity. Treating the cardiovascular problems in diabetics must be undertaken with caution. Special consideration must be given with respect to the ionic and metabolic changes associated with diabetes. For example, although ACE inhibitors and calcium channel blockers are suitable agents, potassium channel openers cause myocardial preconditioning and decrease the infarct size in animal models, but they inhibit the insulin release after glucose administration in healthy subjects. Furthermore, potassium channel blockers abolish myocardial preconditioning and increase infarct size in animal models, but they protect the heart from the fatal arrhythmias induced by ischemia and reperfusion which may be important in diabetes. For example, diabetic peripheral neuropathy usually presents with silent ischemia and infarction. Mechanistically, parasympathetic cardiac nerve dysfunction, expressed as increased resting heart rate and decreased respiratory variation in heart rate, is more frequent than the sympathetic cardiac nerve dysfunction expressed as a decrease in the heart rate rise during standing.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Role of elevated lipids in diabetic cardiomyopathy

Diabetic cardiac dysfunction appears to be associated with an increase in plasma lipids especially triglycerides. Drugs that lower plasma lipids will usually improve cardiac performance in diabetic rats. More recently, an association between decreased cardiac glucose metabolism resulting from increased utilization of fatty acid metabolism in the diabetic myocardium has been suggested. Of the drugs tested, those drugs that decreased plasma lipids and improved cardiac glucose metabolism also improved cardiac performance. Drugs, such as clofibrate, which decreased triglyceride levels and did not enhance cardiac performance in diabetic rats will be examined in the near future in order to test the hypothesis.